The present invention pertains to a device and method for treating heart disease. More particularly, the present invention is directed to a method and device for treating congestive heart disease and related valvular dysfunction.
Congestive heart disease is a progressive and debilitating illness. The disease is characterized by a progressive enlargement of the heart.
As the heart enlarges, the heart is performing an increasing amount of work in order to pump blood each heart beat. In time, the heart becomes so enlarged the heart cannot adequately supply blood. An afflicted patient is fatigued, unable to perform even simple exerting tasks and experiences pain and discomfort. Further, as the heart enlarges, the internal heart valves cannot adequately close. This impairs the function of the valves and further reduces the heart""s ability to supply blood.
Causes of congestive heart disease are not fully known. In certain instances, congestive heart disease may result from viral infections. In such cases, the heart may enlarge to such an extent that the adverse consequences of heart enlargement continue after the viral infection has passed and the disease continues its progressively debilitating course.
Patients suffering from congestive heart disease are commonly grouped into four classes (i.e., Classes I, II, III and IV). In the early stages (e.g., Classes I and II), drug therapy is the commonly proscribed treatment. Drug therapy treats the symptoms of the disease and may slow the progression of the disease. Importantly, there is no cure for congestive heart disease. Even with drug therapy, the disease will progress. Further, the drugs may have adverse side effects.
Presently, the only permanent treatment for congestive heart disease is heart transplant. To qualify, a patient must be in the later stage of the disease (e.g., Classes III and IV with Class IV patients given priority for transplant). Such patients are extremely sick individuals. Class III patients have marked physical activity limitations and Class IV patients are symptomatic even at rest.
Due to the absence of effective intermediate treatment between drug therapy and heart transplant, Class III and IV patients will have suffered terribly before qualifying for heart transplant. Further, after such suffering, the available treatment is unsatisfactory. Heart transplant procedures are very risky, extremely invasive and expensive and only shortly extend a patient""s life. For example, prior to transplant, a Class IV patient may have a life expectancy of 6 months to one-year. Heart transplant may improve the expectancy to about five years.
Unfortunately, not enough hearts are available for transplant to meet the needs of congestive heart disease patients. In the United States, in excess of 35,000 transplant candidates compete for only about 2,000 transplants per year. A transplant waiting list is about 8-12 months long on average and frequently a patient may have to wait about 1-2 years for a donor heart. While the availability of donor hearts has historically increased, the rate of increase is slowing dramatically. Even if the risks and expense of heart transplant could be tolerated, this treatment option is becoming increasingly unavailable. Further, many patients do not qualify for heart transplant for failure to meet any one of a number of qualifying criteria.
Congestive heart failure has an enormous societal impact. In the United States alone, about five million people suffer from the disease (Classes I through IV combined). Alarmingly, congestive heart failure is one of the most rapidly accelerating diseases (about 400,000 new patients in the United States each year). Economic costs of the disease have been estimated at $38 billion annually.
Not surprising, substantial effort has been made to find alternative treatments for congestive heart disease. Recently, a new surgical procedure has been developed. Referred to as the Batista procedure, the surgical technique includes dissecting and removing portions of the heart in order to reduce heart volume. This is a radical, new and experimental procedure subject to substantial controversy. Furthermore, the procedure is highly invasive, risky and expensive and commonly includes other expensive procedures (such as a concurrent heart valve replacement). Also, the treatment is limited to Class IV patients and, accordingly, provides no hope to patients facing ineffective drug treatment prior to Class IV. Finally, if the procedure fails, emergency heart transplant is the only available option.
Clearly, there is a need for alternative treatments applicable to both early and later stages of the disease to either stop the progressive nature of the disease or more drastically slow the progressive nature of congestive heart disease. Unfortunately, currently developed options are experimental, costly and problematic.
Cardiomyoplasty is a recently developed treatment for earlier stage congestive heart disease (e.g., as early as Class III dilated cardiomyopathy). In this procedure, the latissimus dorsi muscle (taken from the patient""s shoulder) is wrapped around the heart and chronically paced synchronously with ventricular systole. Pacing of the muscle results in muscle contraction to assist the contraction of the heart during systole.
While cardiomyoplasty has resulted in symptomatic improvement, the nature of the improvement is not understood. For example, one study has suggested the benefits of cardiomyoplasty are derived less from active systolic assist than from remodeling, perhaps because of an external elastic constraint. The study suggests an elastic constraint (i.e., a non-stimulated muscle wrap or an artificial elastic sock placed around the heart) could provide similar benefits. Kass et al., Reverse Remodeling From Cardiomyoplasty In Human Heart Failure: External Constraint Versus Active Assist, 91 Circulation 2314-2318 (1995).
Even though cardiomyoplasty has demonstrated symptomatic improvement, studies suggest the procedure only minimally improves cardiac performance. The procedure is highly invasive requiring harvesting a patient""s muscle and an open chest approach (i.e., sternotomy) to access the heart. Furthermore, the procedure is expensivexe2x80x94especially those using a paced muscle. Such procedures require costly pacemakers. The cardiomyoplasty procedure is complicated. For example, it is difficult to adequately wrap the muscle around the heart with a satisfactory fit. Also, if adequate blood flow is not maintained to the wrapped muscle, the muscle may necrose. The muscle may stretch after wrapping reducing its constraining benefits and is generally not susceptible to post-operative adjustment. Finally, the muscle may fibrose and adhere to the heart causing undesirable constraint on the contraction of the heart during systole.
German Utility Model Patent Application DE 295 17 393 U1 describes a pericardium prosthesis made from a biocompatible, non-expansible material, or at least hardly expansible material which surrounds the heart. While the pericardium prosthesis prevents overexpansion of the wall of the heart, the action is deployed suddenly when the volume of the heart reaches the volume enclosed by the prosthesis. The sudden deployment may adversely affect the heart.
PCT application WO 98/58598 describes an elastic pouch for at least partially enveloping a heart. The elastic pouch always exerts the same force, substantially irrespective of its expansion, on the heart, so that the heart is always relieved of substantially the same tension irrespective of its volume. The volume of the pouch in the unexpanded state is smaller than the volume of the heart at the stage of minimum filling, thereby ensuring that the pouch is in contact with the heart in all stages of expansion. While such a force may help eject blood during systole, such a force could interfere with ventricle filling during diastole.
Commonly assigned U.S. Pat. No. 5,702,343 to Alferness dated Dec. 30, 1997 (corresponding to PCT Published Application No. WO 98/14136) teaches a jacket to constrain cardiac expansion during diastole. The present invention pertains to improvements to the invention disclosed in the ""343 patent.
According to a preferred embodiment of the present invention, a method and device are disclosed for treating congestive heart disease and related cardiac complications such as valvular disorders. The invention includes a jacket of biologically compatible material. The jacket defines an internal volume dimensioned for an apex of the heart to be inserted into the volume and for the jacket to be slipped over the heart. The jacket has a longitudinal dimension between upper and lower ends sufficient for the jacket to surround a lower portion of the heart preferably between, or even including the valvular annulus of the heart and the ventricular lower extremities. The jacket is adjustable on the heart to snugly conform to an external geometry of the heart and assume a maximum adjusted volume for the jacket to constrain circumferential expansion of the heart beyond the maximum adjusted volume during diastole and to permit unimpeded contraction of the heart during systole.
The jacket is preferably constructed from a flexible material having a multi-axial expansion less than about 30% when said material is exposed to a load up to about 5 pounds per inch (9 Newtons per centimeter). More preferably, the expansion of the material along a first axis is between about 30% and 40% when exposed to a uniaxial load between about 0.1 pounds per inch (0.2 Newtons per centimeter) to about 0.5 pounds per inch (0.9 Newtons per centimeter) with no lateral constraint and the expansion of the material along a second axis perpendicular to the first axis of said material is between about 20% and 30% when exposed to a uniaxial load between about 0.1 pounds per inch (0.2 Newtons per centimeter) to about 0.5 pounds per inch (0.9 Newtons per centimeter) with no lateral constraint. Most preferably, the jacket material is oriented such a that the first axis (i.e., the more compliant direction) extends parallel to the longitudinal axis (AA-BB) of the heart.